The broad objective of this work is to understand the basis of formation of the ventricular chamber of the heart. This project specifically considers two distinct processes: how do cardiac muscle cells (cardiomyocytes) expand in number (proliferate), and how do coronary blood vessels form. These processes are related by virtue of being controlled by signals from the outer layer of the heart, a cell type called the epicardium. This project seeks to understand the role and mechanistic basis of these signals, primarily utilizing genetically engineered mice, explanted embryonic mouse tissue, and tissue culture cells to conduct this research.